An analysis of Pluto occultation light curves using an atmospheric radiative–conductive model

Zalucha, Angela M.; Gulbis, A. A. S.; Zhu, Xun; Strobel, D. F.; Elliot, J. L.

doi:10.1016/j.icarus.2010.08.018

Cited by 47 publications

(63 citation statements)

References 35 publications

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“…!" 32.9 AU this has been used in previous modeling (Strobel et al, 1996;Zalucha et al, 2011) and the viscosity exponent is close to the best-fit power law to Lemmon's conductivity.The time stepping procedure for the fluid-Jeans model is described in Chapter 2.The time step is set to between 0.1-1 days (~10 4 -10 5 s) depending on solar activity, with the smaller step required for the higher solar heating cases, and when the larger upper boundary is used. To save on computation time, the heating rates are recalculated every 10 time steps.…”

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confidence: 79%

“…. Hence, the UV heating contribution to the atmospheric structure starts near the upper boundary of Strobel et al (1996) andZalucha et al (2011). In the thermosphere models of Strobel (2008), Tucker et al (2012), and, the methane IR heating was simply parameterized.…”

Section: Heating'discussion'mentioning

confidence: 99%

“…The best-fit solutions of Zalucha et al (2011) have largest residuals between 10% to 50% depending on occultation event, so the UV activity may have a small affect if this model were used to fit stellar occultation curves. The temperature gradient at the surface changes by only 2% due to UV activity, and the escape rate in the presence of significant UV heating has a non-negligible contribution to the energy conservation in the atmosphere.…”

Section: No Uv Min Med Maxmentioning

confidence: 99%

“…The escape rate calculated using the fluid-DSMC model is nearly the same as the fluid-Jeans results given in Table ( The escape rate enhancement obtained in the full atmosphere fluid-DSMC model is between 2.1 and 2.5 times the Jeans rate as compared to the 1.6-2.3 enhancement given in Table ( I studied the sensitivity of the atmosphere to lower boundary parameters. Zalucha et al (2011) found the stellar occultation were particularly sensitive to surface pressure and the 64 methane mixing ratio. I used the solar minimum UV heating rates, and I held the enhancement in the Jeans escape rate fixed at 2 to approximate the DSMC escape rate.…”

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confidence: 96%

“…The resulting temperature structure compared well with those inferred from stellar occultation. Zalucha et al (2011) used this radiative conductive model to constrain the free parameters (surface pressure, radius, temperature and mixing ratios) by fitting to stellar occultations. They found similar values to those given in Lellouch et al (2009) and Lellouch et al (2011).…”

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confidence: 99%

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Simulating Pluto's Atmosphere with Hybrid Fluid/Kinetic Models

Erwin

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Recent and planned spacecraft exploration of the planets and moons of our solar system have greatly increased interest in atmospheric escape. The Cassini spacecraft is currently improving our understanding of the upper atmosphere of Saturn's large moon Titan, in 2014 the Maven spacecraft will begin to orbit Mars to study its upper atmosphere and atmospheric loss, and in 2015 the New Horizons spacecraft will have a close flyby encounter with Pluto. My motivation has been to produce an accurate model of Pluto's atmosphere, which includes atmospheric loss by escape. The results will be both predictive for and tested against data obtained during the New Horizon encounter. By accurately describing the present loss rates, one can hope to eventually be able to extrapolate back in time in order to describe the long-term evolution of Pluto's atmosphere. Doing this accurately for a planet for which we will have in situ spacecraft data will then guide our ability to model atmospheres for a large number of exoplanets observed orbiting other stars for which there is only remote sensing data.Constraints on Pluto's atmosphere have been obtained through modeling and a few stellar occultation events in the last few decades. These have set a surface pressure range of 6.5-24 microbar of the primarily nitrogen atmosphere, with a methane mixing ratio of ~0.5%. Carbon monoxide has been detected as a trace species out to ~4 planetary radii, suggesting an atmosphere that is much more extended than predicted. Typically hydrodynamic models have been applied to describe escape from planetary bodies such as Pluto and Titan. Such models require solving the fluid equations out to very large distances from the planet in order to enforce boundary conditions. However, it is known ii through molecular kinetic simulations that at some finite distance above the surface the fluid equations fail to describe the gas properties accurately as the atmosphere transitions into the largely collisionless exosphere. To accurately capture the nature of the escape and structure of Pluto's thermosphere and exosphere, I have developed a model of Pluto's upper atmosphere by connecting a fluid model, using radiative heating models relevant for the thermosphere and stratosphere, to a molecular kinetic model. Using this hybrid model I have shown that the atmosphere is much more extended than previously predicted and the escape is not supersonic, as in comet or stellar atmospheres. Rather, it is closer to the evaporative Jeans model of escape.Pluto's lower atmosphere or upper atmosphere have typically been modeled separately, without considering the interactions between these two regimes. Therefore, Ihave developed a self-consistent model of Pluto's full atmosphere, including both the stratospheric radiative heating and cooling that prevail in the lower atmosphere, as well as the UV heating and the cooling by atmospheric escape. These reach a sensitive balance in the upper atmosphere. The stratospheric processes included non-LTE IR radiative heating and cooli...

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confidence: 79%

Section: Heating'discussion'mentioning

confidence: 99%

Section: No Uv Min Med Maxmentioning

confidence: 99%

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confidence: 96%

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confidence: 99%

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Simulating Pluto's Atmosphere with Hybrid Fluid/Kinetic Models

Erwin

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Solar wind at 33 AU: Setting bounds on the Pluto interaction for New Horizons

et al. 2015

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NASA's New Horizons spacecraft flies past Pluto on 14 July 2015, carrying two instruments that detect charged particles. Pluto has a tenuous, extended atmosphere that is escaping the planet's weak gravity. The interaction of the solar wind with Pluto's escaping atmosphere depends on solar wind conditions as well as the vertical structure of Pluto's atmosphere. We have analyzed Voyager 2 particles and fields measurements between 25 and 39 AU and present their statistical variations. We have adjusted these predictions to allow for the Sun's declining activity and solar wind output. We summarize the range of SW conditions that can be expected at 33 AU and survey the range of scales of interaction that New Horizons might experience. Model estimates for the solar wind standoff distance vary from~7 to~1000 R P with our best estimate being around 40 R P (where we take Pluto's radius to be R P = 1184 km).

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